Temperature-stabilized electronic devices

ABSTRACT

Vanadium oxide exhibits a substantial and relatively abrupt change in conductivity as the temperature of the material is varied through a particular characteristic temperature (about 68* C.). In accordance with our invention, a vanadium oxide resistor is employed as a temperature-sensing element in the control circuit of a heater to stabilize the operating temperature of an electronic circuit at about 68* C. over a wide range of ambient temperatures.

United States Patent Inventors Carl N. Berglund Plainfield; Martin P.Lepselter, New Providence, both of NJ.

Appl. No. 865,747

Filed Oct. 13, 1969 Patented Oct. 19, 1971 Assignee Bell TelephoneLaboratories, Incorporated Murray Hill, NJ.

TEMPERATURE-STABILIZED ELECTRONIC DEVICES 12 Claims, 4 Drawing Figs.

[56] References Cited UNITED STATES PATENTS 3,050,638 8/1962 Evans et al307/310 3,149,298 9/1964 Handelman 338/22 3,286,138 11/1966 Shockley...317/235 3,358,152 12/1967 Alexakis... 307/310 3,444,399 5/1969 Jones307/310 Primary Examiner.lames D. Kallam Attorneys R. .I. Ciuenther andArthur J. Torsiglieri ABSTRACT: Vanadium oxide exhibits a substantialand relatively abrupt change in conductivity as the temperature of thematerial is varied through a particular characteristic temperature(about 68 C.). In accordance with our invention, a vanadium oxideresistor is employed as a temperature-sensing element in the controlcircuit of a heater to stabilize the operating temperature of anelectronic circuit at about 68 C. over a wide range of ambienttemperatures.

BACKGROUND OF THE INVENTION This invention relates generally tosemiconductor devices; and, more particularly, to such devices whichinclude provision for stabilizing their operating temperature forimproved operating characteristics and improved reliability.

Most conventional semiconductor devices are inherently teiiipeiaturesensitive; and, accordingly, these exhibit wide variations in certain oftheir operating characteristics in response to variations in theiroperating temperatures. Inasmuch as variations in ambient temperatureproduce corresponding changes in operating temperature if the device isnot in some way temperature stabilized, the design of semiconductorcircuits suitable for operation in a wide range of ambientternperaturesis complicated by having to account for these variations.

In addition to causing variations in operating characteristics,temperature variations can cause other problems in semiconductordevices. For example, differences in thermal coefficient of expansionamong the composite of difierent materials usually employed can causeintolerable strains and stresses when'wide temperature variations areexperienced. Further, at relatively low temperatures, e.g., roomtemperature and below, moisture can become absorbed on the surface of adevice and can act as an electrolyte for interelectrode plating whenoperating voltages are applied to the device. This interelectrodeplating is believed to be a major cause of device failure at the lowertemperatures.

Heretofore, in the prior art, balanced bridge temperature controlsystems have appeared most promising from the standpoint of reliabilityand accuracy. See, e.g., U.S. Pat. No. 3,449,599, issued June 10, 1969,to .l. J. Henry. However, these systems usually have been adapted formaximum flexibility and accuracy and not, apparently, for economy ofeither physical space or cost.

SUMMARY OF THE INVENTION In view of the above and other considerations,it is an object of our invention to provide simple and inexpensive meansfor stabilizing the operating temperature of an electronic circuit at anelevated operating temperature.

It is a further object of our invention to reduce the size of atemperature control system.

To these and other ends, in accordance with our invention, there isprovided a vanadium oxide (vo,) resistor as a temperature-sensingelement in combination with electrically energizable heat-generatingmeans for stabilizing the operating temperature of an electronic circuitover a wide range of ambient temperatures.

It is well known that certain crystalline compounds of the 3- dtransition metals exhibit a substantial and relatively abrupt change inconductivity as the temperature of the material is varied through aparticular characteristic temperature. See, e.g., U.S. Pat. No.3,149,298, issued Sept. 15, 1964, to E. T. Handelman, and assigned tothe assignee hereof. As is well known in the art, the 3-d transitionelements are those elements numbered 21 through 28 in the Periodic Tableof the Elements. In particular, monocrystalline samples of V0, haveexhibited changes in conductivity by a factor of greater than 10 over atemperature interval of 2 C. at about 68 C. In deposited thin films of Vthe conductivity transition usually occurs in a somewhat broadertemperature interval (several degrees centigrade) centered at about 68C. and is not so substantial or greater). See, De.g., Structural andElectrical Properties of Vanadium Oxide Thin Films," G. A. Rozgonyi etal., Journal of Vacuum Science and Technology, Vol. 5, No. 6, p.l94,l968. However, even using films having this less sharply definedconductivity transition, a temperature control system in accordance withour invention is capable of stabilizing the operating temperature of anelectronic circuit to within several degrees centigrade; and this ismore than sufficient for many applications.

More specifically, now, in accordance with a presently preferredembodiment of our invention, there is provided a vanadium oxide resistorin the bias circuit of a simple heater, De.g., a transistor, to maintainthe controlled circuit at an elevated operating temperature. Both theheater and the vanadium oxide resistor advantageously are disposed inintimate thermal energy transfer relationship with the controlledcircuit for optimum responsiveness. For example, both the vanadium oxideresistor and the heater advantageously are disposed in a monolithicsemiconductor wafer along with the controlled circuitry.

In operation, as temperature increases through about 68 C. theconductivity transition of V0, causes the V0 resistor to assume arelatively low resistance which causes the heater to be biased off.Conversely, as temperature decreases through about 68 C. the V0,resistor reverts to its high-resistivity state causing the heater to bebiased on. This heating pushes the temperature back toward 68 C.

It will be apparent that a temperature control system in accordance withour invention, as summarized hereinabove, is

operable only for ambient temperatures below about 68 C. since nocooling apparatus has been described. Further, it will also be apparentthat cooling apparatus can be connected to our control system such thatthe cooling apparatus turns on when the V0, switches to thelow-resistance resistance state and so that the heater turns on when thev0, switches to the high-resistance state.

However, cooling apparatus usually is complex, expensive, and bulky;and, therefore, is usually undesirable for use with miniaturizedsemiconductor devices to which our invention primarily is directed.Heating apparatus, on the other hand, can be virtually as simple, smalland inexpensive as desired. Further, for many applications, the ambienttemperature is not expected to exceed 68 C. (about F.); and so for theseapplications cooling apparatus would be superfluous.

BRIEF DESCRIPTION OF THE DRAWING The aforementioned and other objects,features, and advantages of our invention will be more readilyunderstood from the following detailed description taken in conjunctionwith the accompanying drawing in which:

FIG. 1 is a 'graph of conductivity versus temperature for a typicalmaterial exhibiting the conductivity transition utilized by ourinvention;

FIG. 2 shows a schematic diagram of a simple control circuit inaccordance with a presently preferred form of our invention;

FIG. 3 shows a cross section of one small portion of a semiconductorwafer including one possible integrated circuit embodiment of thecontrol circuit of FIG. 2; and

FIG. 4 shows a generalized cross section of a temperaturestabilizedintegrated-circuit device in accordance with a presently preferred formof our invention.

It will be appreciated that for simplicity and clarity of explanationthe figures have not necessarily been drawn to scale.

DETAILED DESCRIPTION More particularly now, with reference to FIG. I, aportion 11 of the graph shows a substantially. constant and relativelylow conductivity at temperatures below the characteristic temperature Tof transition. At temperatures above T portion 12 of the curve shows asubstantially constant and relatively high conductivity. At T,, thetransition temperature, conductivity ideally increases (or decreases)abruptly, as indicated by portion 13 of the curve. In imperfect crystalsand thin films, however, the conductivity transition usually occurs overa temperature interval (several degrees 'centigrade), as shown byportion 14 of the curve. Particularly in thin films, there is usuallysome hysteresis in the conductivity versus temperature curve, as shownby portion 15 of FIG. I. This hysteresis is at least partially due tobuilt-in stresses in the Referring now to FIG. 2, there is shown aschematic diagram of a simple control system in accordance with apresently preferred form of our invention. A transistor 21 is shown withthe common node of a series pair of bias resistors 22 and 23 connectedto its base terminal. Resistor 22, connected between the collector andbase of transistor 21, is selected from the well-known resistors whichmaintain a fairly constant resistance over the temperatures to beexperienced, De.g., a carbon resistor or any of a variety of impedancedevices commonly used in integrated circuits. Resistor 23 includes amaterial which undergoes a conductivity transition such as describedwith reference to FIG. 1. Vanadium oxide (V0,) is presently preferredfor resistor 23, for reasons discussed hereinbelow.

In operation, a voltage (|+V) is applied to the collector of transistor21 and the emitter is grounded. The resistor values are adjusted so thattransistor 21 is biased on at temperatures below T (conductivitytransition temperature). The power dissipated in transistor 21 providesheat energy which tends to raise the temperature of both resistors. Theresistor values are also adjusted so that when the temperature ofresistor 23 increases through T the resistance of resistor 23 decreasesto a value small enough to cause transistor 21 to be biasedsubstantially off.

Thus, for ambient temperatures less than T,, the operating temperatureof any circuits in intimate thermal relationship with transistor 21 andresistor 23 will oscillate about T The amplitude of this thermaloscillation will depend upon the abruptness of the conductivitytransition of resistor 23 and upon the amount of thermal hysteresis inthat resistor.

In a particular embodiment which was constructed and tested, resistor 22was about 7,000 ohms; resistor 23 varied from about 30,000 ohms at atemperature below T to about 50 ohms at a temperature above T and +V wasabout 7.5 volts. The operating temperature of transistor 21 wasstabilized to within a few degrees centigrade at about 68 C. over anambient from room temperature to about 70 C.

It will be appreciated that it would be desirable for some applicationsto provide a higher stabilized operating temperature, De.g., up to about200 C. so that a greater range of ambient temperatures could thereby beaccommodated. However, no practical thin film materials are presentlyknown to exhibit such a conductivity transition within the range oftemperatures from about 70 C. to 200 C. One material, silver sulfide(Ag,S), is known to exhibit a conductivity transition at about 170 C.;however, this material exhibits ionic conductivity due to mobile silverions under applied electric fields. Because of the instability resultingfrom this ionic conductivity, silver sulfide will generally beundesirable for most uses in accordance with our invention. Of course,if a suitable material is discovered, it may be substituted for resistor23, as desired, within the scope of our invention.

With reference now to FIG. 3, there is shown a portion of asemiconductor wafer 31 including one of the many possible integratedcircuit embodiments of the control circuit of FIG. 2. A semiconductivebulk portion 32, e.g., of P-type silicon, includes a pattern oflocalized conductivity type zones within the bulk and a composite oflayered patterns formed thereover. N-type zone 33 provides thecollector; P-type zone 34 provides the base; and N-type zone 35 providesthe emitter for transistor 21. P-type zone 36 provides fixed resistor22. N*-type zone 37 provides a low-resistance path, within the bulk,around the aforementioned zones.

A pattern of dielectric material, e.g., silicon oxide, provideselectrical isolation between electrodes on the surface of thesemiconductor; and, additionally, provides a substrate upon which apattern of vanadium oxide 39 can be formed to provide resistor 23.

An electrode 40 provides electrical connection to N -type 37 and thus tothe collector of the transistor. Electrode 41 provides electricalconnection to the emitter of the transistor. Electrode 42 provides acommon electrical connection to: the base of the transistor (zone 34);one end of resistor 22 (zone 36); and one end of resistor 23 (pattern39). Electrode 43 provides electrical connection to the end of resistor23; and electrode 44 provides electrical connection between the otherend of resistor 22 and the collector of transistor 21 via semiconductivezone 37.

A plurality of methods for fabricating semiconductor integrated circuitssimilar to that shown in FIG. 3 are well known in the art. However, abrief description of some possible techniques for forming the vanadiumoxide layers may aid the practitioner inasmuch as the particulartechnique used should depend upon the particular circuit in which thevanadiurn oxide resistor is used and upon the desired accuracy oftemperature control.

It is known in the art that thin films of vanadium oxide formed onamorphous substrates, e.g., silicon oxide, usually do not exhibit asharply defined conductivity transition. For example, as reported in theaforementioned publication by Rozgonyi et al. a thin film of vanadiumoxide formed directly on glass by reactive sputtering exhibited aconductivity transition by a factor of only 77 with an hysteresis of 7C. As will be appreciated, this type of characteristic is suitable forthose applications in which the operating temperature need not be soprecisely controlled.

However, if more precise control is desired, a technique, such asdisclosed in the copending U.S. application Ser. No. 776,732, filed Nov.18, 1968, now U.S. Pat. No. 3,491,000, issued Jan. 20, 1970, andassigned to the assignee hereof, may be advantageous. As disclosedtherein, if a thin layer of tantalum oxide (T 0 is formed over theamorphous substrate prior to forming the vanadium oxide layer, theconductivity transition of the vanadium oxide is more sharply defined.

A variety of techniques for forming the vanadium oxide also are wellknown in the art. For example, one can deposit a thin layer of vanadiumand then convert this layer to its oxide, as disclosed by R. J. Powellin Stanford Electronics Laboratories Report No. 5220-1, May, 1967.Alternatively, reactive sputtering may be used to deposit directly thevanadium oxide layer, as disclosed in the aforementioned publication byR02- gonyi et al. Still another technique includes reactive evaporationof vanadium in an oxygen atmosphere followed by an annealing process, asdisclosed in Philips Res. Rept., Vol. 22, p.170 (1967) by K. vanSteensel et al.

With particular relation now to integrated circuits, FIG. 4 shows ageneralized cross section of a presently common type of integratedcircuit technology. A semiconductor wafer 51 having conductive beam-leadconnections 52 and 53 is registered with and attached to corresponding,preformed conductive portions 54 and 55 on an insulating substrate 56,e.g., a circuit board, as disclosed, for example, in U.S. Pat. No.3,426,252, issued Feb. 4, 1969, to M. P. Lepselter and assigned to theassignee hereof.

As presently contemplated, a control circuit embodiment, such as shownin FIG. 3, can be included as a small portion of wafer 51 in FIG. 4.There may be a plurality of wafers 51, each including its own controlcircuit, attached to a single insulating substrate. In this manner, thegood thermal conduction properties of each semiconductor wafer enableclose thermal relationship between the control circuit and thecontrolled circuits in each wafer.

Alternatively, there may be provided a separate wafer 51 providing thetemperature control circuit mounted on a single insulating substratealong with other wafers which do not con tain their own controlcircuits. In this case, the electrode connections (52-55) and theinsulating substrate (56) are advantageously selected to provide closethermal relationship between the wafer(s) which contain the controlcircuit (s) and those wafers which do not.

What is claimed is:

1. Apparatus for maintaining an electronic device at a stabilizedelevated operating temperature comprising:

A body of material including the device whose temperature is to bestabilized;

Electrically energizable heat-generating means mounted in intimatethermal energy transfer relationship with the body for heating thedevice; and

control means including temperature sensitive means connected to theheat-generating means for controlling the rate of heat generation in theheat-generating means; said temperature sensitive means comprising aresistor including material selected from the group consisting of the3-d transition materials which exhibit a relatively abrupt change inconductivity at a transition temperature corresponding essentially tothe desired elevated operating temperature, and being located to haveits recited in claim 1 wherein the temperature means includes aresistor, controlled by the temperature of the body.

2. A device recited in claim 1 wherein the temperature sensitive meanscomprises vanadium oxide.

3. A device as recited in claim 1 wherein the temperature means includesa resistor, the operative part of which consists essentially of vanadiumoxide.

4. An electronic device adapted for operation at a stabilized elevatedtemperature comprising:

a body of material including the device whose temperature is to bestabilized;

electrically energizable heat-generating means mounted in close thennalenergy transfer relationship with said body for heating said body;

a vanadium oxide resistor in close thermal energy transfer relationshipwith said body for sensing the temperature of said body; and

circuit means to which said vanadium oxide resistor is connected forcontrolling the rate of heat generation in the heat-generating means.

5. A device as recited in claim 4 wherein the vanadium oxide resistorconsists essentially of vanadium dioxide.

6. A temperature stabilized semiconductor integrated circuit devicecomprising in combination:

a body of silicon including at least one device whose temperature is tobe stabilized; and

means for stabilizing the operating temperature of the device comprisingelectrically energizable heat-generating means in combination with atemperature sensitive means which includes a resistor consistingessentially of vanadium oxide.

7. A device as recited in claim 6 wherein the vanadium oxide resistorcomprises a relatively thin layer of vanadium oxide disposed over thesurface of the body.

'8. Means for stabilizing the temperature of a body of material at anelevated temperature comprising in combination:

a transistor disposed in close thermal energy transfer relationship withthe body for heating the body; and

a vanadium oxide resistor connected in shunt with the base emitterjunction of the transistor for controlling the rate of heat generationin the transistor; said vanadium oxide resistor also disposed in closethermal energy relationship with the body sothat its temperature iscontrolled by the temperature of the body.

9. Apparatus as recited in claim 8 further comprising means for biasingthe transistor and the resistor by an amount sufficient to elevate thetemperature of the body to the vanadium oxide transition temperature.

10. An electronic device adapted for operation at a stabilized elevatedtemperature comprising:

A body of material including the device whose operating temperature isto be stabilized;

Electrically energizable heat-generating means mounted in close thermalenergy transfer relationship with said body for heating said body;

temperature sensitive means connected to the heat-generating means andmounted in close thermal energy transfer relationship with the body forcontrolling the rate of heat generation in the heat-generating means,the temperature sensitive means including a resistor, an operative partof which is a material which exhibits a conductivity transition at aredictable transition temperature; and means for lasing theheat-generating means and the resistor by an amount sufficient toelevate the temperature of the body, the heat-generating means, and theresistor to the transition temperature.

11. Apparatus as recited in claim 10 wherein the resistor is coupled tothe heat-generating means in such a way that heat is generated when thetemperature of the resistor is substantially below the transitiontemperature and heat is not generated when the temperature of theresistor is substantially above the transition temperature so that theoperating temperature is stabilized about the transition temperature.

12. Apparatus as recited in claim 11 wherein the conductivity transitionmaterial is a film of vanadium oxide having a transition temperature atabout 68 C.

1. Apparatus for maintaining an electronic device at a stabilizedelevated operating temperature comprising: A body of material includingthe device whose temperature is to be stabilized; Electricallyenergizable heat-generating means mounted in intimate thermal energytransfer relationship with the body for heating the device; and controlmeans including temperature sensitive means connected to theheat-generating means for controlling the rate of heat generation in theheat-generating means; said temperature sensitive means comprising aresistor including material selected from the group consisting of the3-d transition materials which exhibit a relatively abrupt change inconductivity at a transition temperature corresponding essentially tothe desired elevated operating temperature, and being located to haveits recited in claim 1 wherein the temperature means includes aresistor, controlled by the temperature of the body.
 2. A device recitedin claim 1 wherein the temperature sensitive means comprises vanadiumoxide.
 3. A device as recited in claim 1 wherein the temperature meansincludes a resistor, the operative part of which consists essentially ofvanadium oxide.
 4. An electronic device adapted for operation at astabilized elevated temperature comprising: a body of material includingthe device whose temperature is to be stabilized; electricallyenergizable heat-generating means mounted in close thermal energytransfer relationship with said body for heating said body; a vanadiumoxide resistor in close thermal energy transfer relationship with saidbody for sensing the temperature of said body; and circuit means towhich said vanadium oxide resistor is connected for controlling the rateof heat generation in the heat-generating means.
 5. A device as recitedin claim 4 wherein the vanadium oxide resistor consists essentially ofvanadium dioxide.
 6. A temperature stabilized semiconductor integratedcircuit device comprising in combination: a body of silicon including atleast one device whose temperature is to be stabilized; and means forstabilizing the operating temperature of the device comprisingelectrically energizable heat-generating means in combination with atemperature sensitive means which includes a resistor consistingessentially of vanadium oxide.
 7. A device as recited in claim 6 whereinthe vanadium oxide resistor comprises a relatively thin layer ofvanadium oxide disposed over the surface of the body.
 8. Means forstabilizing the temperature of a body of material at an elevatedtemperature comprising in combination: a transistor disposed in closethermal energy transfer relationship with the body for heating the body;and a vanadium oxide resistor connected in shunt with the base emitterjunction of the transistor for controlling the rate of heat generationin the transistor; said vanadium oxide resistor also disposed in closethermal energy relationship with the body so that its temperature iscontrolled by the temperature of the body.
 9. Apparatus as recited inclaim 8 further comprising means for biasing the transistor and theresistor by an amount sufficient to elevate the temperature of the bodyto the vanadium oxide transition temperature.
 10. An electronic deviceadapted for operation at a stabilized elevated temperature comprising: Abody of material including the device whose operating temperature is tobe stabilized; Electrically energizable heat-generating means mounted inclose thermal energy transfer relationship with said body for heatingsaid body; temperature sensitive means connected to the heat-generatingmeans and mounted in close thermal energy transfer relationship with thebody for controlling the rate of heat generation in the heat-generatingmeans, the temperature sensitive means including a resistor, anoperative part of which is a material which exhibits a conductivitytransition at a predictable transition temperature; and means forbiasing the heat-generating means and the resistor by an amountsufficient to elevate the temperature of the body, the heat-generatingmeans, and the resistor to the transition temperature.
 11. Apparatus asrecited in claim 10 wherein the resistor is coupled to theheat-generating means in such a way that heat is generated when thetemperature of the resistor is substantially below the transitiontemperature and heat is not generated when the temperature of theresistor is substantially above the transition temperature so that theoperating temperature is stabilized about the transition temperature.12. Apparatus as recited in claim 11 wherein the conductivity transitionmaterial is a film of vanadium oxide having a transition temperature atabout 68* C.